1. Field of the Invention
The present invention relates to primers for small arms ammunition which have covered flash holes. More specifically, the present invention relates to covering multiple flash holes in a unitary primer assembly where the battery cup and anvil have been formed integrally.
2. Description of the Prior Art
Conventional primers for small arms ammunition usually include three separate metal components: a primer cup, an anvil and a battery cup. The primer cup contains an impact sensitive explosive priming mixture for igniting the propellant powder charge of the ammunition cartridge. The battery cup serves as a support for the anvil and primer cup and contains at least one flash hole. The flame and heat produced by the detonation of priming mixture upon impact to the anvil will travel through the flash hole to ignite the propellant powder.
The flash holes of conventional primers may or may not be covered. The advantages of a covered flash hole have long been recognized. A closed flash hole prevents the explosive priming mixture from dusting out of the primer after it has been charged and also reduces static electricity hazards.
Another advantage is that a closed flash hole prevents propellant powder from entering the priming mixture chamber. This permits the use of fine grain propellant powder without having the fine powder sift into the battery cup through an open flash hole. The presence of fine propellant powder within the battery cup is objectionable because the ignition of powder within the relatively confined area of the battery cup may cause excessive pressure and blow the primer cup rearwardly away from the battery cup.
A closed flash hole construction also permits rapid identification of pre-fired primers. Such primers can be recognized readily by the condition of the flash hole cover.
The potential for flame-induced mass detonation of primers packed in bulk is also reduced significantly by the covered flash hole construction. Mass detonation is an almost instantaneous chain reaction type of explosion which can occur when one primer is ignited and in turn ignites adjacent primers. Covered flash holes prevent the flame of an accidentally ignited primer from entering adjacent primers and thus reduces the risk of mass detonation.
Two methods are employed generally for covering flash holes in conventional primers. The first involves the insertion of a paper disc directly over the flash hole inside the battery cup. The disc covers the bottom surface of the battery cup and is secured in place by the anvil which is inserted subsequently. The second method utilizes a liquid such as a lacquer. The lacquer is wicked over the flash hole from the outside of the battery cup and allowed to dry.
The paper disc method offers several technical and safety advantages over the liquid technique for covering flash holes during the manufacturing process. Safety in production is improved when the paper disc is used since the primer can be final assembled while the priming mixture is wet and thus less sensitive. The moisture can then be driven off through the paper disc at a later time to sensitize the priming mixture when exposure of personnel to accidental discharge is minimized. Moreover, working with paper results in a cleaner and more desirable overall production operation than the use of lacquer type liquid. The latter, for example, requires controlling the minute application and drying of the lacquer liquid.
More recently, technical developments in the field of complex progressive dieing tools have led to primer configurations wherein the anvil and battery cup are formed integrally from a single piece of metal. An example of such an integral anvil-battery cup (hereinafter referred to as "anvilled battery cup" or "ABC") primer is described in U.S. Pat. No. 4,029,015 granted on June 14, 1977 to M. Lachaussee and A. Maigret. The anvilled battery cup construction of this patent is illustrated in FIGS. 5-7 and includes multiple flash or vent holes at the bottom of the battery cup arranged around an axially and inwardly extending pressed part forming the anvil. Because the anvil is integral with the battery cup and also because the anvil is shaped like a fluted cone, covering the multiple flash holes in this type of primer presents unusual problems not present in conventional primers.
There are several possible solutions to covering the flash holes in anvilled battery cup primers. An integral metal flap can be provided at the flash hole such as described in U.S. Pat. Nos. 3,352,240 and 3,363,563, both granted to G. R. Eckstein on Nov. 14, 1967 and Jan. 16, 1968, respectively, and assigned to the same assignee as the present invention. Although the integral metal flap designs of these patents offer numerous advantages, they add an additional degree of complexity to the already complex progressive drawing techniques necessary to form the integral anvil and battery cup metal piece.
The lacquer type liquid technique discussed earlier is presently being used in some instances to cover the flash holes of anvilled battery cup primers similar to that described in the aforenoted U.S. Pat. No. 4,029,015. This technique, however, continues to suffer the same disadvantages encountered with its use in conventional primers described earlier.
The use of paper as the covering medium would appear to be the preferred method of covering flash holes in anvilled battery cup primers, as it is in conventional primers. Since the anvil is formed integral with the battery cup, however, it is not possible simply to insert a paper disc into the bottom of the battery cup as may be done when working in conventional primer assemblies where the anvil is inserted after the paper disc and also serves to secure the disc in place over the flash holes. Moreover, the irregular shape of the fluted conical anvil in the anvilled battery cup construction shown in FIGS. 5-7 makes it unusually difficult to insert a covering medium such as paper along the bottom of the battery cup rapidly and cover the flash holes effectively in a high speed production operation.